1. Field of the Invention (Technical Field)
The present invention relates to transmutation of nuclear waste.
2. Background Art
Geologic storage of nuclear waste has been for the past thirty years the primary plan for permanent storage of nuclear waste worldwide. However, concerns about the effectiveness of confinement, the loss of the large energy content of the plutonium waste, the accumulation of thousands of tons of weapons-useful plutonium in the stored waste, and the possibility of recriticality of the waste in permanent storage have delayed the implementation of geologic storage worldwide. At present, no nation has Identified a permanent site for geologic storage of high-level nuclear waste and implementation of geologic waste storage anywhere is at least a decade away. Several nations have attempted to address this problem by destroying the waste using technologies such as mixed oxide (MOX) waste burning in conventional light water reactors (LWRs) or in fast breeder reactors converted for waste burning. While some gains are possible using these approaches, the impact on the waste problem is either minor or the time scale for making a significant impact is much longer than a human generation. Therefore there is no consensus that destruction of waste using conventional nuclear technology is practical for improving geologic storage significantly.
Over the last decade, scientists have proposed schemes for improved waste destruction using accelerator-driven reactor-like systems and some of these concepts have been patented. Typically, such systems offer gains by using an accelerator to supplement the number of neutrons beyond those available in an ordinary reactor and thereby to obtain more complete destruction or burn-up of the waste. An accelerator also may be used to allow operation outside of technical constraints imposed by the criticality requirement of normal reactors. The following patents disclose technology related to reduction and production of nuclear matter.
U.S. Pat. No. 5,774,514, entitled "Energy Amplifier for Nuclear Energy Production Driven by a Particle Beam Accelerator," to Rubbia, issued Jun. 30, 1998. This patent discloses a method for producing energy from a nuclear fuel material contained in an enclosure. A high energy particle beam is directed into the enclosure for interacting with a heavy nuclei target to produce high energy spallation neutrons, such target comprising bismuth and/or lead, wherein the bismuth and/or lead are in a molten state. The spallation neutrons are multiplied in steady subcritical fission conditions. This patent also discloses the use of a plurality of fuel bodies each encapsulated in a shell of a solid-phase moderator, such moderator comprising graphite.
U.S. Pat. No. 5,768,329, entitled "Apparatus for Accelerator Production of Tritium," to Berwald, issued Jun. 16, 1998. This patent discloses a process for preparing or breeding tritium gas from dense molten lithium alloy, such as an eutectic lead lithium alloy. The molten lithium alloy serves as a target material for a high energy particle beam whereby the beam's high energy protons interact with the target to generate a neutron flux. The molten state lead lithium alloy circulates past the beam impact area and through a heat exchanger to recover thermal energy.
U.S. Pat. No. 5,545,797, entitled "Method of Immobilizing Weapons Plutonium to Provide a Durable Disposable Waste Product," to Ewing et al., issued Aug. 13, 1996. This patent discloses a method of fixation and immobilization of plutonium whereby the plutonium is fixed in the form of either PuO.sub.2 or Pu(NO.sub.3).sub.4 and is mixed with ZrO.sub.2 and SiO.sub.2.
U.S. Pat. No. 5,513,226, entitled "Destruction of Plutonium," to Baxter et al., issued Apr. 30, 1996. This patent discloses a method of using plutonium in a manner so as to render it no longer suitable for employment in a device to create nuclear detonation. The first three steps of the ten step method comprise forming plutonium oxide spheroids, coating the spheroids with a multi-layer fission-product retentive coating and disposing the coated spheroids in a plurality of graphite block elements. Fissioning of the fissle plutonium nuclides occurs through neutrons primarily in the thermal range.
U.S. Pat. No. 5,499,276, entitled "Method for Minor Actinide Nuclides Incineration," to Wakabayashi, issued Mar. 12, 1996. This patent discloses a method of minor actinide incineration by adding neptunium of minor actinide nuclides separated from spent fuel to a reactor core fuel of a fast reactor and adding americium of the separated minor actinide nuclides and rare earth elements to radial and/or axial blankets and/or shield of the fast reactor.
U.S. Pat. No. 5,160,696, entitled "Apparatus for Nuclear Transmutation and Power Production using an Intense Accelerator-generated Thermal Neutron Flux," to Bowman, issued Nov. 3, 1992, expired Nov. 6, 1996 due to failure to pay maintenance fees. This patent discloses an apparatus using a high energy proton beam and a spallation target to generate high thermal neutron fluxes wherein the target comprises a high Z-material such as a liquid lead-bismuth eutectic mixture. The high thermal neutron fluxes are used to burn-up higher actinide nuclear waste and rapid burn-up of fission product waste.
U.S. Pat. No. 4,721,596, entitled "Method for Net Decrease of Hazardous Waste Materials," to Marriott et al., issued Jan. 26, 1988. This patent discloses a method for decreasing reactor waste materials through use of a thermal neutron flux whereby neutrons for transmutation are produced from a fission or non-fission, e.g., fusion, source.
U.S. Pat. No. 4,309,249, entitled "Neutron Source, Linear-Accelerator Fuel Enricher and Regenerator and Associated Methods," to Steinberg et al., issued Jan. 5, 1982. This patent discloses an apparatus for producing fissle material using a high energy particle beam, nuclear fuel elements and a liquid metal target material. For example, a proton accelerator produces high energy protons that interact with a liquid lead-bismuth metal that surrounds LWR fuel elements placed in pressure tubes whereby the interaction of the beam and liquid metal produces neutrons. The neutrons are absorbed by the nuclides in the fuel elements and transformed to fissle material.
U.S. Pat. No. 3,349,001, entitled "Molten Metal Proton Target Assembly," to Stanton, issued Oct. 24, 1967. This patent discloses a thermal nuclear apparatus having a molten metal high nergy proton target, e.g., molten lead, surrounded by a blanket of fertile material and a recirculating coolant.
To date, none of the accelerator-driven systems have received the funding necessary to construct and operate a system demonstrating enhanced waste burning capabilities. One reason seems to be that the addition of an expensive accelerator and extensive chemical separations increase the cost of these transmutation concepts well beyond that of conventional reactor technology which is itself too expensive for deployment for waste burning. Since geologic storage adds only incrementally to nuclear electric power costs, transmutation should also add only incrementally to the cost. Therefore, if an accelerator must be added, other components or operations normally required for nuclear power should be eliminated to keep costs under control.